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Full text of "Text Book Of Mechanical Engineering"

Appendix VL

iiS7

Thermal Efficiency of the Engine. The work obtained from
coal in terms of its calorific value is much greater in any internal-
combustion engine than in the steam engine, though the real
improvement is a matter of recent years. The following list
compares oil, gas, and steam engines :

THERMAL EFFICIENCY.
(Ralgp of B.H.P. to Calorific Value.)

ENGINE FUEL.
	B.H.P.
	o/
 1/0

Oil   ...........................
	AO tO  CO
	26 to 30

Blast-furnace gas     ......
	7O tO 72 
	20 to 26

Producer gas   ............ I Natural gas ..................
	/ w  tv^  y *. ^
 ioo to 370
 50 to 150 40 to 600
	20 tO 25
 14 to 20
 22 tO  2 Z A

Lififhtinsr eras   ...............
	10 to 50
	20 to 25

Steam (simple reciprocating) ,.     (triple) ...............
	150 to 380
 IOOO tO 2OOO
	12 tO  15
 1 6 to 17

(turbines) ......       ,
	Similar
	


	
	

A series of diagrams are given in Pig. 1022, to shew the dis-
tribution of heat per cent, in various engines, and the effect of
different fuels on that distribution is both curious and instructive.

The jacket and exhaust wastes appear almost to interchange,
so a saving in jacket water means a hotter exhaust, while the
liberal use of water, as in the Premier engine, gives the best
possible result in every respect. Professor Burs tail's experiments
on account of the LM.E. Research Committee are represented on
the extreme right. They varied between the full and dotted line
indications, the best results appearing to be due to high speed
combined with small clearance space.

Improvements in the Engine. Water cooling has been carried
ta a greater extent than heretofore. ,In large engines not only